import java.util.HashMap;

/*
 * @lc app=leetcode.cn id=1 lang=java
 *
 * [1] 两数之和
 *
 * https://leetcode-cn.com/problems/two-sum/description/
 *
 * algorithms
 * Easy (47.66%)
 * Likes:    7734
 * Dislikes: 0
 * Total Accepted:    849.9K
 * Total Submissions: 1.8M
 * Testcase Example:  '[2,7,11,15]\n9'
 *
 * 给定一个整数数组 nums 和一个目标值 target，请你在该数组中找出和为目标值的那 两个 整数，并返回他们的数组下标。
 * 
 * 你可以假设每种输入只会对应一个答案。但是，你不能重复利用这个数组中同样的元素。
 * 
 * 示例:
 * 
 * 给定 nums = [2, 7, 11, 15], target = 9
 * 
 * 因为 nums[0] + nums[1] = 2 + 7 = 9
 * 所以返回 [0, 1]
 * 
 * 
 */

// @lc code=start
class Solution {
    /* public int[] twoSum(int[] nums, int target) {
        for (int i = 0; i < nums.length; i++) {
            for (int j = i+1; j < nums.length; j++) {
                if (nums[i] + nums[j] == target) {
                    return  new int[] {i , j};
                }
            }
        }
        return null;
    } */

    
    /* public int[] twoSum(final int[] nums, final int target) {
        final Map <Integer ,Integer>   numad= new HashMap <Integer ,Integer> ();
       
        for (int i = 0; i < nums.length; i++) {
            numad.put(target - nums[i], i);
        }
        
        for (int i = 0; i < nums.length; i++) {
            if (numad.containsKey(nums[i]) && numad.get(nums[i]) != i) {
                return new int[] {i , numad.get(nums[i])};
            }
        }
        return null;
        
    } */

    public int[] twoSum(final int[] nums, final int target) {
        HashMap<Integer, Integer> hashMap = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            if (hashMap.containsKey(nums[i])) {
                return new int[] {hashMap.get(nums[i] ) , i};
            }
            hashMap.put(target - nums[i], i);
        }
        return nums;
    }
}
// @lc code=end

